Liquid crystal display devices with low operating power are in widespread use not only in mobile devices but also in stationary type devices. As such a liquid crystal display device, there exists a liquid crystal display device in which: digital signals indicative of grayscales of respective pixels are supplied to a data signal driving circuit, and the data signal driving circuit applies voltages, corresponding to values of the digital signals, to data signal lines, thereby controlling grayscales displayed in the pixels.
In the liquid crystal display device, data for determining a voltage applied to each pixel of the display panel is transferred as a digital signal. Thus, when a bit width of grayscale data indicative of a grayscale is enlarged so as to display a finer grayscale, a circuit size or a computing amount of a circuit for processing the digital signal is increased. On the other hand, when the bit width is narrowed by truncating less significant bits so as to reduce the circuit size or the computing amount, a pseudo outline occurs in an image displayed in a display panel, so that display quality is significantly deteriorated.
Here, in order to realize an image display device which can improve the display quality with a simple circuit while preventing occurrence of the pseudo outline, Japanese Unexamined Patent Publication No. 337667/2001 (Tokukai 2001-337667)(Publication date: Dec. 7, 2001) discloses a technique in which: after adding a noise to the digital signal, the less significant bits are truncated. Specifically, when a digital signal of n bit (n is a natural number) is inputted as a video signal, a first signal processing section 516 shown in FIG. 26 performs γ correction with respect to the digital signal of n bit, so as to convert the digital signal into a digital signal of m bit (m>n: m is a natural number). Further, a second signal processing section 517 adds a noise signal to the digital signal of m bit that has been outputted from the first signal processing section 516, and then truncates a less significant (m−Q) bit (Q≦n: Q is a natural number), and outputs a digital signal of remaining Q bit to a data signal line driving circuit 514 of the display panel. Further, the data signal line driving circuit 514 outputs, via a data signal line, a voltage corresponding to the digital signal of Q bit that has been outputted from the second signal processing section 517, thereby controlling the grayscales displayed in the pixels.
In this arrangement, a bit width (Q bit) of the digital signal outputted from the second signal processing section 517 is set to be shorter than a bit width (m bit) of the digital signal outputted from the first signal processing section 516. As such, its circuit arrangement is simplified as compared with a case where the data signal line driving circuit 514. Thus, it is possible to process the digital signal outputted by the first signal processing section 516.
Further, the second signal processing section 517 adds the noise signal, and then truncates the less significant bits. Thus, unlike the case of merely truncating the less significant bits, pixels adjacent to each other are not greatly different from each other in terms of the displayed grayscale. As a result, it is possible to realize an image display device which can improve the display quality with a simple circuit while preventing occurrence of the pseudo outline.
While, compared with a CRT (Cathode-Ray Tube) and the like, a response speed of the liquid crystal display device is slow. Thus, there is a case where the response is not completed in a rewriting time (16.7 msec), corresponding to an ordinary frame frequency (60 Hz), due to a transition grayscale.
A method has been adopted, in which a driving signal is modulated and driven so as to emphasize grayscale transition from a grayscale indicated by previous grayscale data to a grayscale indicated by current grayscale data (see Japanese Unexamined Patent Publication No. 116743/2002 (Tokukai 2002-116743)(Publication date: Apr. 19, 2002) for example).
For example, in case where grayscale transition from a previous frame FR (k−1) to a current frame FR (k) is “rise”, a voltage is applied to the pixel so as to emphasize the grayscale transition from a grayscale indicated by the previous grayscale data to a grayscale indicated by the current grayscale data. More specifically, a voltage whose level is higher than a voltage level indicated by video data D (i, j, k) of the current frame FR (k) is applied to the pixel.
As a result, when the grayscale varies, a luminance level of the pixel sharply increases and approaches a vicinity of a luminance level corresponding to the video data D (i, j, k) of the current frame FR (k) in a short period compared with a case where a voltage whose level is indicated by the video data D (i, j, k) of the current frame FR (k) is applied. Thus, even when the response speed of the liquid crystal is low, it is possible to improve the response speed of the liquid crystal display device.
Further, Japanese Patent Publication No. 2650479 (Date of Patent: Sep. 3, 1997) discloses a display device in which: a transmittance curve is made or predicted in accordance with signal data of at least three sequential fields that are applied to arbitrary pixels, and the signal data of the sequential fields are corrected when the transmittance curve deviates from a desired transmittance curve by a predetermined value or more.
Specifically, as shown in FIG. 27, in the display device 501a, a data input device 521 stores video data to the pixels are stored in a field memory 522. Further, a data correction device 523 refers to the field memory 522, and corrects the video data of the field memory 522 when a difference between an ideal transmittance and an actually predicted transmittance is larger than a predetermined threshold value. Further, a data output device 524 sequentially reads out thus corrected video data of the field memory 522, so as to drive pixels (not shown).